# Crossing the Bridge together [closed]

Two friends each weighing 150 lbs arrive at a Rope bridge 100 yards long.

The warning sign at the start of the bridge informs it can hold only a maximum of 325 lbs of weight at any given second, otherwise it instantly collapses endangering any crossing humans.

Both wish to cross the bridge simultaneously while each of them carries three sacks of potatoes one of which is 2 lbs, the second is 3 lbs while the third sack is 11 lbs.

How will they be able to accomplish this in one single trip together?

Please Please clearly state your assumptions. Water under the bridge. Just do not give up based on some prejudices or previous experience. This is a Classical Problem to Solve.

Hint

Socrates : What Plato is going to say next is a Lie. Plato: Whatever Socrates mentioned is the truth.

• Will the collapsing bridge endanger any crossing potatoes? – user2357112 supports Monica Oct 28 '15 at 21:25
• How the hell is that a hint? – Deusovi Oct 29 '15 at 11:04
• The Potato Paradox only applies in a specific situation, and it's not about potatoes.You also didn't say these were hydrated such that 99% of eit weight is water. – Deusovi Oct 29 '15 at 13:23
• Thinking outside the box does not mean making arbitrary assumptions. The potato paradox doesn't have anything to do with potatoes, but it does pertain to percentages of weight. You mentioned potatoes, but not percentages of weight. – Deusovi Oct 29 '15 at 13:30
• @Deusovi I regret not being reachable with comment replies to clarify and guide the expected answer. Will do better next time with next puzzle. Your patience and guidance is much appreciated. – kanchirk Oct 29 '15 at 13:33

Do to PHYSICS a bridge is under most strain when weight is applied to the middle. As we are only a couple of pounds over the weight, all that we need to do is make sure that all the weight is never applied to the middle, and the bridge should be fine.

Tie the potato sacks together to form a long line from lightest to heaviest 2-2-3-3-11-11

Now the friends walk together (holding hands i guess) and drag the chain of sacks behind them. Potato sacks are big, so the extra weight is almost 20 feet behind. This is more than enough to make sure we never have 325 in the center

The standard solution is

juggling

but that won't work since

the force exerted by your hand has to be greater than the weight, and due to Newton's third law, that force will be the same as the force you exert on the bridge in addition to your weight.

• add the gravity when the sack are falling when juggling – Mekalikot Oct 29 '15 at 0:30

I may just be pedantic but here's my take:

It doesn't state that the friends are carrying identical bags:

"One of which is 2 lbs the second is 3 lbs while the third sack is 11 lbs."

So if one friend is carrying those three bags adding up to 16 lbs the other could be carrying any combination of 3 bags adding up to 9 lbs making a total of 325 lbs as the two friends together weigh 300 lbs themselves

• I was thinking along the same lines, but my take was a little bit different. It says that "each of them carries three sacks of potatoes", but not that each of them carries three separate sacks. So the answer is for them to carry the sacks together. two 150 pound people, who together are carrying one 11-pound, one 3-pound, and one 2-pound sack adds up to 150+150+11+3+2 = 316 pounds, safely under the limit. – Rauwyn Oct 29 '15 at 14:35

Given that each of them has identical bags of potatoes(11-3-2 each) and not given that they are on one side of the bridge the solution is trivial:

They are on the different sides of that bridge. Each of them can leave his bags on his side and take the bags of the other guy on the other side and continue walking. Their total weight is 300 lbs, which is less than 325 that a bridge can handle

Assuming that these 2 friends are healthy but not entirely fit...

Get 1 friend to make a 30 pound makeshift dumbbell from the potatoes and have him/her to start working out for 30 minutes. Have the other friend go for a run for 30 minutes. 1 pound of combined water weight will be shed and they will be able to cross the bridge.

If they don't want to wait...

Have one of them do continuous gag reflexes until they throw up.

This 100 yard rope bridge is a real tourist attraction and, as a result, a souvenir/gift shop has opened up right next to the bridge. As luck would have it, they've just received a brand new canister of helium for the gift balloons. The standard gift shop canister of helium contains 250 cubic feet of helium which would be enough to support the weight of 8 pounds of potatoes plus the string and balloons (see here).

Here is my solution

Get a long rope and tie all the sacks together. Then throw the sack to the river under the bridge keeping the end of the rope in hand. Cross the bridge together and then pull up the potatoes. Even though the potatoes get sink in water, the effective weight of the potatoes will be considerably less than the actual weight.